Allow the parsing of OBO files

[yum-yab]

For example the bioregistry saves it's ontologies in the .obo format.

It would be nice to allow the parsing/loading of such files into Archivo, but currently rapper/rdflib do not support such files.

Also then the discovery process for the bioregistry needs to be adapted (add new key download_obo).

[cthoyt]

FYI the Bioregistry only keeps metadata about ontologies, it is not creating nor maintaining ontologies itself.

[matentzn]

There is no urgent need to parse OBO files as all OBO (Foundry, at least) ontologies are required to provide a primary RDF/XML release!

[cthoyt]

There are plenty of non obo foundry ontologies listed in Bioregistry that only have an obo flat file, eg, cellosaurus